The present invention relates to a fuse production method, a fuse, a circuit board production method and a circuit board.
Fuses are used to prevent the occurrence of circuit breakdown due to an inflow of excess current caused by a failure, or the like, in an electronic device. Specifically, a fuse has a fuse film bonded to a substrate, and when an abnormal current flows in a circuit, the fuse film is blown to cut off the circuit to prevent the circuit from being broken.
When a bonding between the substrate and the fuse film is weak, there is a possibility that the fuse film is peeled from the substrate and breaks even when no abnormal current flows. In particular, since conduction occurs repeatedly through the fuse film, expansion and contraction of the fuse film frequently occurs between the fuse film and the substrate because the fuse film and the substrate have a different expansion coefficient with respect to the rise in temperature, and so the fuse film is easily peeled from the substrate. Therefore, there is a demand to firmly bond the fuse film to the substrate in order to prevent the fuse film from being peeled off.
Patent Document 1 (Japanese Patent Application Publication No. 2008-200875) proposes, in order to enhance an adhesion between an insulating substrate and a metal thin film in a circuit board, a method of causing a metal oxide to exist at a contact interface between an insulating resin layer, which exists between the insulating substrate and the metal thin film, and the metal thin film.
As electronic devices incorporating fuses are becoming smaller and lighter, further downsizing and weight reduction of the fuses are required. However, when the technique of Patent Document 1 is applied to a small fuse, it is necessary to make the surface roughness of the contact interface between the insulating resin layer and the metal thin film be 100 (nm) or less, which incurs a great cost.
Further, the production method disclosed in Patent Document 1 includes performing a heat treatment in an atmosphere containing an oxidizing agent. On this occasion, it is necessary to adjust the oxygen concentration to about 20 to 2000 (ppm), which requires expensive equipment.